Biasing potential supply circuit



July 16, 1940.

SOURCE S VIV- F. R. NORTON BIASING POTENTIAL SUPPLY CIRCUIT Filed Oct. 5, 195'? INVENTOR By. ER. NOR 701v wag, AZ/fl k ATTORNEY Patented July 16, 1940 e I yifUNlTED STATES PATENT OFFICE BIASING POTENTIAL SUPPLY CIRCUIT at I 1 v Frank R. Norton, Pequannock, N. J., assignor to Bell Telephone Laboratories, Incorporated, New

York, N. Y., a corporation of New York Application October 5, 1937; Serial No. 167,375

zcClaims. (c1. 250 m)v This invention relates to biasing potential supthe deflecting plates of a cathode ray tube through ply circuits and more particularly to such cirsuitable coupling condensers and a resistance, cuit's when embodied in sweep circuits for telethe mid-point of this resistance being connected vision scanning or cathode ray oscillography. to the anode of the cathode ray tube. In the In Patent No. 2,180,365 of F. R. Norton, patnovel circuit arrangement according to this inented November 21, 1939, there is disclosed a vention the grid biasing potential for the gassweep circuit for use in television scanning. The filled tubes is obtained from variable cathode invention described herein comprises'novel means resistances and large by-pass condensers, instead forobtaining and applying biasing potential withof from grid batteries as in the sweep circuit to out'the use of batteries for certain of the elecshown in Patent No. 2,180,365, supra. By making tron discharge tubes used in that circuit which the cathode resistances variable, it is possible to circuit is an improved balanced sweep circuit easily adjust the grid bias to a suitable value for utilizing gas-filled electron discharge devices. p op functioning, of the Circuit w up e 1 An object of this invention is to provide an discharging of the gas-filled tubes occurs in synl5 improved'circuit arrangement for biasing the conchronism. c 16 trol electrode with respect to the cathode of elece invention Will be described more in detail tron" discharge tubes. having reference to the accompanying drawing A further object is to provide a circuit arrangewhich Shows a balanced s p Circuit embodying ment utilizing the sweep circuit condenser disthis invention.

charge currentto provide the biasing potential of The drawing shows a balanced sweep circuit 0 an electron discharge tube which controls said which may be used, for example, as a suitable condenserdischarge, source for generating saw-tooth voltages to be In one embodiment of this invention now to be ppl ed to a p of deflecting plates of a cathode described by way of example, adouble sweep cirray oscillograph or a television receiving tube to 3 cuit is employed, that i a, sweep irc it in hi h cause deflection of the cathode ray beam in onev plurality of gas-filled grid-controlled electron direction, as for example, in a horizontal direcdischarge devices used for producing the (115- tion. A similarcircuit, differing only from this charge strokes in the generation of the saw-tooth O in the Value Of the circuit Constants, y be wave forms have their plate circuits in series and used to produce vertical deflection. The circuit '30 havetheir grid biasing potentials provided by the Comprises condensers Ill and l I of relatively small 0 novelfcir'cuit arrangement of this invention. By p y having their Common al l2 00nthis sweep circuit arrangement the available oute e to ground; d means for chargi and put voltage may be approximately doubled. Andischarging these condensers simultaneously. other advantage of this double circuit is that it e charging Circuit for e er 0 Comproduces a balanced output without the necessity prises a Source Of Potential Which ay be for amplifiers or a floating power supply, In obtained from a battery or a suitable rectifying other words, in this circuit the power supply may device, and a constant current device 14 which be grounded without producing unbalance. In may be a saturated diode or a pentode. Preferits preferred form the sweep circuit comprises ably, the device l4 comprises a pentode having a d twocondensers in series with their common teratho l5, an a de s, a control grid IT, a screen minal grounded, a constant current device such as d a d a Supp grid I11 vSeries. With a r'nulti grid electron discharge device having the plate circuit of the device 14 is the biasing refeedback circuits on one or more of its grids and s s ce Which y be adjustable s b asa source of current for charging up each coning resistance 2|] is also in the input circuit bedenser in a substantially linear manner with retween the cathode. l5 and the control grid l1 and spect to time, and two grid-controlled gas-filled y means this. arrangement y ease in electron discharge devices which may be, for exvoltage in the plate circuit of the device I caused ample, of the type generally .known as Thyraby the increasein charge across the condenser tron? tubes, having their plate circuits in a series n wh h tends to reduce the p e current will 6 circuit including the condensers, and suitable decrease the bias of the control grid I! and tend means such as a transformer having two secondto keep the current through the tube at a conary windings for discharging the Thyratron" stant value. Thus the rate of charge of the 'contubes' simultaneously. The change in voltage denser'lll tends to be constant. The biasing reacross the condensers due to their charging and sistanceZfl may be, if desired, arranged i a feeddischarging may be applied,'for' example; across back relationwvithresDeetto the screen grid I8. 55

A battery 2| is also used in this circuit to produce a constant direct current bias between the cathode and the screen grid I8. The effect of the feed back on the screen and control grid is cumulative. For a more complete description of the method of operation of pentode tubes having feedback circuits on one or more of their grids to produce a constant condenser charging rate, reference is made to Patent No. 2,180,364 of F. R. Norton, patented November 21, 1939.

The circuit for charging the condenser I I comprises a battery and a constant current source 3I having a cathode 32, an anode 33, a control grid 34, a screen grid and a suppressor grid 36. A biasing resistor 31 is connected in the plate circuit and also in the circuit between the oathode 32 and the grid 34 in a manner similar to the connection for the resistance 20 described above. This biasing resistance 31 is also connected in a circuit between the cathode 32 and the screen grid 35, this circuit also including a battery 38 Which is similar to battery 2| described above. Battery 38 may obviously be a part of battery 30, if desired, and both may be replaced by a rectifier or other source of direct current potential.

In order to have a balanced circuit, the capacities between point A and ground and point B and ground represented by the condensers II] and I I and including the external connections thereof should be equal, and also the constant current devices I4 and 3| and their connections should be similar.

The circuit for discharging the condensers Ill and II at periodic intervals comprises a source of synchronizing signals 40 which is connected to the primary winding M of the transformer 42 which has two secondary windings 43 and 44, connected respectively to the grids of Thyra' tron tubes TI and T2 through potentiometers 45 and 46. The synchronizing signals supplied by the source 40 may be produced by an oscillator or other device which periodically produces current of suitable wave form which may be impressed upon a cathode ray oscillograph or used in a television system.

The source 40 may be located at the transmitter or at the receiver and may take any one of a variety of well-known forms. For example, if the circuit now being described were used in connection with a cathode ray tube at the receiver, and a scanning disc were used to generate the image and synchronizing signals at the transmitter, an arrangement for generating the syn chronizing signals may be used similar to the one described in Patent No. 2,050,363, of E.. R. Morton, patented August 11, 1936. If a cathode ray device is used at the transmitting station, the return pulses of the horizontal or the vertical deflecting circuits may beused to generate the synchronizing signals for the corresponding sweep circuits at the receiving station.

The Thyratron tubes TI and T2 are of the gas-filled electron discharge type comprising respectively a cathode 48, an anode 4'9 and a grid for tube TI, and a cathode 5I, an anode 52 and a grid 53 for tube T2. Novel biasing circuits are connected in the grid-cathode circuits of these Thyratron tubes. These circuits comprise a condenser 54 shunted by a variable resistance 55 placed in the grid-cathode circuit of tube TI, and a condenser 58 shunted by a resistance 59, which may be either fixed or variable, placed in the grid-cathode circuit of tube T2. The values of these condensers and resistances 2,207,940 I I k I depend upon various factors such as the other circuit constants and the frequency of operation of the sweep circuit. However, it is important that the capacity of condensers 54 and 58 be very large as compared with that of condensers I0 and II whose values are determined by the circuit constants and the frequency of the sweep circuit. plate circuits of tubes TI and T2, respectively, in order to limit the peak discharge currents through the Thyratron tubes. The plate circuits of tubes TI and T2 are connected in a series circuit which includes resistance 51, condensers It and II, condenser 58 and resistance 59 in parallel, plate circuit of tube T2, resistance 56, condenser 54 and resistance 55 in paralleLand plate circuit of tube TI. The common terminal of condenser 54 and resistance 55 remote from the cathode of the tube TI and the terminal'of resistance 56 remote from the anode 52 of tube T2 are connected to ground. By means of this arrangement the voltage between points A and B is twice the voltage between either of these points and ground.

For coupling the points A and B to the defiecting plates 68 and SI of the cathode ray ,tube 52, an amplifier or a suitable wide-band trans former might be used, or as shown in the draw ing, coupling condensers 63 and 64 and coupling resistances 55 and 66 may be utilized. Condensers 53 and 54 are preferably of equal capacity and resistances 65 and 66 should be equal. The mid-point 51 of the high resistances 65 and 65 is connected to the anode 68 of the cathode ray device 62. By means of this balanced circuit arrangement, the average of the voltages ap: plied to the plates 58 and GI always equals the potential of the anode 68.

In producing the, biasing potential for tubes TI and T2, the condenser ID is charged through a circuit from positive voltage source I3 through the anode-cathode circuit of constant current tube I4, and condenser II is charged through the anode-cathode circuit of tube 3] from negative voltage source 38. impressed upon the input transformer 42 causes the potentials of the grids of TI and T2 to become suificiently high to cause the tubesto break down and to discharge condensers I0 and I I, condenser IEl discharging through tube TI into condenser 54 connected in the grid-cathode circuit Resistances 51 and 56 are placed in the Once per cycle the wave of tube TI, and condenser I I discharging through tube T2 into condenser 58 in the grid-cathode circuit of tube T2. The grid condensers 54' and 58 are shunted by resistances 55 and 59, respec tively. The resistance across one of the condensers is made variable to facilitate bringing the discharging of the two tubes into synchro-' nism, and the resistance across the other con.- denser may also be made variable for making initial circuit adjustment, but need not be, used for routine operating adjustment. The time constant of condenser 54 and resistance 55, and

likewise of condenser 58 and resistance 59, that is, the product of the'capacity times the resistance, is made large compared with the, period of the sweep, and hence the voltage across each of the condensers 54 and 58 decreases very slightly during each cycle of the sweep current. When the tubes TI and T2 break down, the condensers II] and I I quickly discharge to a very low potential. Suitable biasing potential for tubesTI and T2 may be obtained by employing condensers 54 and 58 having capacities of the order of 1000 times the capacity of condensers I0 and II and shunting resistances 55 and 59 having resistances such that the average current through them provides the correct value of bias.

The operation of the circuit as a whole is as follows:

Condensers I0 and H are charged at a substantially linear rate by means of suitable potential sources l3 and and the constant current devices l4 and 3|. At periodic intervals, as for example, at the end of each scanning line, a synchronizing signal is generated by the source and caused to energize the primary 4i of the transformer 42. The voltages in the secondary windings 43 and 44 are made sufficient to overcome the negative bias on the tubes TI and T2 causing these tubes to discharge the condensers l0 and I I simultaneously. The cyclic charge and discharge of the condensers l0 and II produces across the points A and B a voltage wave of sawtooth wave form of the frequency of the syn- A chronizing signals which wave is applied across the plates 60 and 6| of the oscillograph tube 62 by means of the coupling condensers 64 and 63 and the coupling resistances 65 and 66. This voltage wave, as described above, is balanced with respect to the potential of the anode 68, thus eliminating any loss of focus and distortion which would have resulted had the sweep circuit been unbalanced. r

The transformer 42, here shown, is an ordinary audio transformer although it may be an impulse transformer as shown in Patent No. 2,180,365, supra.

In the arrangement shown, amplifiers are not usually necessary in the sweep circuit. However, the circuitmaybe connected to the oscillograph tube by any suitable means such as a condenserresistance coupling, as shown in the drawing, or through other suitable means including amplifiers. Another advantage is that the voltage output is double that which would be produced in single. Thyratron sweep circuits. This advantage is important because the trend at present is toward higher and higher sweep voltages, and because the voltage output of the ,Thyratron tubes is limited in circuits where thefrequency is so high that the time allowed for deionization is very short. Another advantage is the elimination of a floating power supply, that is, one terminal of each of the batteries or potential sources l3 and 30 is connected to ground. A further advantage and novel feature is the elimination of biasing batteries for the Thyratron tubes TI and In an actual circuit operated at a frequency of approximately 5760 cycles per secondv and employing condensers I0 and II each having a capacity of the order of .0007 microfarad and resistances and 66 of the order of 10 megohms and coupling condensers 63 and 64 each having a capacity of the order of 1.0 microfarad, suitable biasing potential was obtained for tubes TI and T2 by connecting in their grid-cathode circuits i condensers 54 and 58 each having a capacity of the order of 0.7 microfarad and shunting resistances 55 and 59, respectively, each having a redeparting from the spirit of the invention, the

scope of the invention being defined by the appended claims.

What is claimed is:

I 1. A voltage source of saw-toothed wave form comprising two equal condensers connected in series, means to charge said condensers at uniform and equal rates, two gas-filled electron discharge tubes each having a cathode, a control grid and an anode, a condenser of relatively large capacityfor each of said tubes shunted 'by'a, respective resistance connected at one terminal thereof to the cathodes of said tubes respectively, means to connect the anode of one of said tubes to the non-common terminal of one of said equal condensers, meansto connect the other terminal of the large condenser which is connected'to the cathode of said one tube to the anode of said other tube and the junction point of said equal condensers, means to connect the other terminal of the large condenser which is connected to the cathode of said other tube to the non-common terminal of the other of said equal condensers, means to intermittently and simultaneously impress voltages on the grid-cathode circuits of said tubes to cause the tubes to break down, and means to vary one of said shunted resistances to cause said tubes to break down simultaneously.

2. A sweep circuit comprising two capacities having a common terminal, means comprising two electron discharge devices for charging said capacities serially substantially simultaneously, means for maintaining said common terminal at a fixed potential, two electron discharge elements each having grid circuits for discharging said capacities substantially. simultaneously, biasing circuits for each of said discharge elementscomprising a capacity shunted by a resistance in the grid circuit of each of, said discharge elements, and means for discharging said first-mentioned capacities periodically through the said secondmentioned capacities to produce voltages to block said discharge elements during the entire charging period of said first-mentioned capacities, and means to vary one of said resistances to cause said discharge elements to discharge said first- 

